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Wednesday, March 18, 2015

Docker + node-red = awesome!

When I first heard about Docker a few weeks ago, I realized how cool it was so I started reading about it right away. Because I kept talking about it, I got tasked at work to look into how we can use it and a couple weeks later, I was deploying 2 linked containers for my team that definitely made our development easier, even if all we are using are database containers, at least for now.

But my first thought when reading about Docker was how could I use it on my Raspberry Pi so I don't keep mixing stuff on the same SD card (which sometimes is not a very good idea, like when I messed up my node-red because I installed an IDE that used an older version of node.js). I know most of the software packages can co-exist without issues but I like to keep things separate so I have a bunch of SD cards now, one for Java projects, one for node-red and a couple more. Docker seems to be the answer to this - at least for my Raspberry Pi B, the As I have are a bit too constrained for Docker but they are dedicated to other projects anyway.

So, I started looking around and the first site that popped up was the excellent resin.io blog, specifically this article. It sounded awesome but it required Arch Linux which I am not familiar with so I decided to wait a bit. As I was researching Docker for work I happened to find a new blog article at hypriot.com that talked about a new Docker compatible image created by this awesome team. This was so great that I immediately cleaned up an SD card and installed this image. As advertised, it worked from the first try: I can't tell you how happy I was to see Docker running on my Pi. And this guys didn't stop at creating the main SD card image, they also published several Docker images made for Raspberry Pi - like I said, an awesome team. Thank you so much for all you do!

I started playing right away with Docker and couldn't wait to come back to it the next day. To my disappointment though, after I restarted my Pi, I kept getting errors no matter what docker command I tried. Given my luck of experience, I thought I broke something (because I also noticed that after changing the password, I started to get a warning every time I used sudo but it turns out this was easily fixed according to this post by adding 127.0.0.1 black-pearl to /etc/hosts) but after quite a lot of digging, I found a post mentioning how to restart the docker daemon - very simple, in hindsight I realize that I should've thought of it:

sudo /etc/init.d/docker start

Now that all was well, I started to work on what I really wanted to do from the start: create a node-red image, because there wasn't one when I started looking into Docker. Of course, there are several node-red images, including this one and since Dave C-J is one the creators of node-red I trust his image the most; but this image is not for Raspberry Pi. I started to work on my own image and I was able to create something fast but after that I spent a few long hours trying to make the rpi-gpio nodes to work without success. In the end, I published my image on Docker Hub but the fact that rpi-gpio nodes was bugging me so I ended up deleting it; I kept the Dockerfile in this gist so I can redo it at any time if I ever feel the need. Which I don't think it will happen because this morning doing yet another search on Docker Hub for "rpi nodered" luck was on my side and I found this image from nieleyde; there is no Dockerfile but I pulled the image immediately and it works great! Thank you so much, nieleyde!

Very important to note in the docker run command provided by nieleyde is the --privileged option (some notes here). When I first started the container, I noticed in the log that the userDir is /root/.node-red; I want to have access to the flows files and also to be able to install more nodes easily without messing up with the original image, so I start the container with a volume option (as detailed in the "Overriding Dockerfile image defaults" section of this article):

This way, everything that happens in the real /root/.node-red user directory is mirrored in my /home/pi/.node-red dir and the other way around, so the flows files, new nodes, library files are shared between these directories. I am not sure if this is the best way but it works for me (well, I still need to check the new added nodes idea but the flows file works as expected so I hope new nodes will as well; also settings.js works fine as I will mention later).

The second thing I did to make it easier: the flows file by default is named flows_<machine_name>.json, for example flows_519c0741e1f0.json. The problem is that the machine name is the actual container short ID and it changes every time when the container restarts so the previous flows are not accessible anymore (the file is still present but is not read because the name doesn't match the machine name anymore). I tried naming the container when running it using --name option, but the name is not used by the flows file, only the container ID is used. To fix this, now that I have access to the user directory via the volume option, I placed a settings.js file in /home/pi/.node-red that changes the flows file name to flows.json. And it worked as I hoped it would: my file overwrites the settings. js file in the node-red install, as described here. Now each time I restart the container the flows file is the same so all my saved flows start immediately; this can be easily seen in the node-red logs: Flows file : /root/.node-red/flows.json.

In conclusion, Docker is really awesome and due to teams like hypriot and users like nieleyde Docker on Raspberry Pi and node-red in Docker are great to use! Thanks to everyone for all the great work!